An ostomy is a surgically-made opening in the body. Ostomies are available in a variety of types including, but not limited to, ileostomies, colostomies and urostomies, as may be needed by a particular patient. Although the discussion below will usually describe the invention with reference to the ostomy resulting from a colostomy procedure, it is to be understood that the invention can be applied to other types of ostomies as well. Further, although the discussion generally considers human patients, the structures described and claimed herein can be useful in non-human mammals as well.
A variety of medical conditions can lead to ostomy surgery, but the four most prevalent are colorectal cancer, diverticulitis, Crohn's Disease and ulcerative colitis. Ostomy surgery for these conditions generally requires the resection of the part or entire colon and/or rectum and the subsequent diversion of the colon or small bowel via an ostomy wherein the end of the remaining healthy portion of the colon or small bowel is brought through the abdominal wall, inverted on itself and sutured in place to form a stoma S. During inactive periods, the stomal tissue pulls together, rather like puckered lips. When waste is to be expelled, the tissue stretches to permit the waste to pass. Although it expands and contracts, the stoma does not have the firm muscle control of the anal sphincter. The muscles M of the remaining segment of colon remain intact and continue to function in a coordinated manner to effectively advance stools distally toward the stoma. However, while the colonic muscles remain relatively unaffected, the storage capacity naturally provided by the rectum and the muscle control provided by the anal sphincters are no longer available. Because of the loss of these key functions, the individual is rendered fecally incontinent (i.e., unable to control the time and place of waste evacuation) and must defecate into an ostomy bag for as long as they have the colostomy.
Fecal management in this manner is generally effective and is the current standard of care for individuals with colostomies. However, the use of ostomy bags often results in these individuals experiencing a variety of problems not ordinarily experienced by the general public (i.e., those with normal defecatory anatomy). These problems include leakage of intestinal gas, mucus, and waste, such as liquid and solid fecal material from around the stoma site. Such leakage not only causes unpleasant odors, but also leads to health problems, such as necrosis of the tissue surrounding the stoma site. The rate of leakage occurrence increases as the bag fills and the resulting weight pulls on the interface between the bag and the abdominal wall. Even when ostomy bags perform optimally, the fear of leakage, odor and the stigma associated with wearing the ostomy bag can have negative effects on the individual's quality of life, particularly their social and psychological well being.
The known art has made a variety of attempts to address these problems with various non-bag devices, without complete success. A number of barrier devices (e.g. foam plugs, catheter ports and inflatable sealing membranes) have been developed which essentially plug or seal the stoma until the user is ready to evacuate. To one degree or another, each of these devices was unable to maintain a safe and/or reliable seal with the intestinal lumen in which they resided, and resulted in leakage of waste around the device, device expulsion and/or tissue damage. Much of the tack of success of these devices can be attributed to the smooth muscle characteristics of the intestinal lumen. Generally, the nature of a smooth muscle lumen is to accommodate to any chronic bolus present within the lumen. In the case where the bolus is a stationary sealing structure, increases in the circumference of the intestinal lumen, as it accommodates, can contribute to leakage of luminal contents around the sealing structure.
To date, only one non-bag ostomy sealing device for the management of colostomies has been made commercially available. The Conseal® Plug made by Coloplast® is a tissue lumen sealing device having an adhesive base plate and a disposable foam plug which permits flatus to pass without the passage of feces, fluid or solid. The plug is supplied in a compressed state within a water-soluble film. The film disintegrates within a few seconds of insertion and the plug expands to its natural size to seal the stoma. The plug is removed to allow for fecal evacuation, after which a new plug is inserted. Although commercialized, the Conseal® Plug suffered from some of the short comings noted above specifically incidents of leakage and device expulsion.
The technical challenges faced in attempting to seal the gastrointestinal ostomy are better understood by reviewing the normal chemical, electrical and mechanical physiological mechanisms effecting colonic motility (i.e., the involuntary muscular activity of the colon which coordinates the movement of digesting materials towards the anus).
The Enteric Nervous System
The nervous system of the human body (and, for that matter, all mammals) has a profound influence on all digestive processes including colonic motility. Some of this control originates from connections between the central nervous system and the gastrointestinal tract, but just as importantly, the gastrointestinal tract is endowed with its own local nervous system, referred to as the enteric nervous system.
The principal components of the enteric nervous system are two networks or plexuses of neurons (the myenteric plexus and the submucosal plexus), both of which are embedded in the wall of the gastrointestinal tract. These enteric neurons secrete an array of chemical neurotransmitters that permit nerve signals to bridge the gap between nerve cells. Certain neurotransmitters are excitatory in nature, stimulating smooth muscle contractions, while others are inhibitory in nature, stimulating smooth muscle relaxation.
While the enteric nervous system can and does function autonomously, normal gastrointestinal function requires communication links between the enteric nervous system and the central nervous system. These links take the form of parasympathetic and sympathetic nerve fibers that connect either the central and enteric nervous systems or connect the central nervous system directly with the gastrointestinal tract. Through these cross connections, the gastrointestinal tract can provide sensory information to the central nervous system, and the central nervous system can affect gastrointestinal function. One example of the nervous interconnections within the gastrointestinal tract is the gastrocolic reflex, where distension of the stomach stimulates evacuation of the colon.
In general, parasympathetic nerve stimulation is excitatory in nature, causing contraction of gastrointestinal smooth muscle and increased gastrointestinal secretion and motor activity. Conversely, sympathetic nerve stimuli typically inhibit these activities.
Colonic Motility and Smooth Muscle
The colon is a dynamic luminal organ. A sectional view of the layers of the colon wall is provided in FIG. 18. Muscles located on the exterior of the colon run along the length thereof, extending and retracting the colon like a rubber band. These muscles contribute to a muscle action called haustral churning which facilitates mixing, fluid absorption and particle cohesion. Interior muscles wrap around the colon in circular bands that distend and contract the colon wall in an action that is similar to opening and closing a fist. Working in concert, these muscles contribute to the principal type of motility called peristalsis (i.e., a distinctive pattern of smooth muscle contraction and relaxation that propels digesting materials distally toward the anus). Ultimately, the peristalsis advances stool into the rectum. When stool fills the rectum, the elastic quality of the wall permits the rectum to expand, creating a sac to accommodate stools just prior to defecation.
All muscles in the colon wall are smooth muscle which has properties distinctly different from skeletal muscle. Unlike skeletal muscle, smooth muscle is not under voluntary control. Smooth muscle fibers are arranged in intertwined, indistinct bundles, aligned in circular and longitudinal layers. Individual smooth muscle fibers are connected to neighboring smooth muscle cells by gap junctions, which allow these cells to be electrically coupled. The important consequence of this electrical coupling is that when an area of smooth muscle becomes depolarized, that depolarization spreads outward through adjacent sections of smooth muscle resulting in a well-coordinated contraction of, for example, an entire ring of circular smooth muscle of the colon.
Electrophysiology of Gastrointestinal Smooth Muscle
Normal gastrointestinal motility results from coordinated contractions of smooth muscle, which in turn derive from two basic patterns of electrical activity across the membranes of smooth muscle cells—slow waves and spike potentials.
Like other excitable cells, gastrointestinal smooth muscle cells maintain an electrical potential difference across their membranes. The resting membrane potential of smooth muscle cells is between −50 and −60 mV. In contrast to nerves and other types of muscle cells, the membrane potential of smooth muscle cells fluctuates spontaneously. Because the cells are electrically coupled, these fluctuations in membrane potential spread to adjacent sections of muscle, resulting in what are called “slow waves”—waves of partial depolarization in smooth muscle that sweep along the gastrointestinal tract for long distances. These partial depolarizations are equivalent to fluctuations in membrane potential of about five to fifteen mV. The frequency of slow waves depends on the section of the gastrointestinal tract—in the small intestine; they occur approximately 10 to 20 times per minute and in the large intestine about three to eight times per minute. Slow wave activity appears to be a property intrinsic to smooth muscle and dependent on nervous stimuli.
Importantly, slow waves are not action potentials and by themselves do not induce contractions. Rather, they coordinate muscle contractions in the gastrointestinal tract by controlling the appearance of a second type of depolarization event (“spike potentials”), which occurs only at the crests of slow waves. Spike potentials are true action potentials that induce muscle contraction. They result when a slow wave passes over an area of smooth muscle that has been primed by exposure to neurotransmitters released in their vicinity by neurons of the enteric nervous system. The neurotransmitters are released in response to a variety of local stimuli, including distension of the wall of the gastrointestinal tract and serve to “sensitize” the muscle by making its resting membrane potential more positive.
It is thus apparent how a particular pattern of motility is achieved. For example, when a large bolus (e.g., ingested food) enters the intestine the bolus distends the intestine, stretching its walls. Stretching stimulates nerves in the wall of the intestine to release neurotransmitters into smooth muscle at the site of distention—the membrane potential of that section of muscle becomes “more depolarized”. When a slow wave passes over the section of smooth muscle exposed to the neurotransmitters, spike potentials form and muscle contraction results. The contraction moves around and along the intestine in a coordinated manner because the muscle cells are electrically coupled through gap junctions. These coordinated muscle contractions work to mix and propel digesting materials distally.
Therefore, in view of the various shortcomings of the known art, the primary goal of the present invention is to overcome the loss of the normal physiological mechanisms associated with the anatomical derangements of a colostomy procedure, and in so doing, allow the individual to be effectively continent.